Desktop Entry icon not appearing: how to diagnose?

[zlmk43qK2]

I know how to work with the CLI. I know how to use vim. I just copied the .desktop contents from this post: http://forum.pine64.org/showthread.php?tid=13383.

Initially i tried putting the .desktop file in ~/.local/share/applications, to no avail. Then i tried putting it in /usr/share/applications with the same result.
Initially, I made the .desktop file executable with

Code:

sudo chmod +x ~/.local/share/applications/themeswitcher.desktop

as instructed in the post, but after taking a closer look at all the other .desktop files in /usr/share/applications, i noticed none of them were executable, so i ran

Code:

sudo chmod 644 dark-light.desktop

to reverse the previous command. Unfortunately, this didn't make a difference either.

here is are the ownership, permissions, location and content.

Code:

mobian@mobian:/usr/share/applications$ la -l | grep dark
-rw-r--r-- 1 root root   270 Mar 14 11:15 dark-light.desktop
mobian@mobian:/usr/share/applications$ cat dark-light.desktop
[Desktop Entry]
Actions=Light;Dark;
Type=Application
Name=Day-Night
GenericName=Theme Switch
Comment=Theme Switch
Icon=contrast
TryExec=gsettings
Exec=notify-send ThemeSwitcher "Long Press for Theme Color Options"
Terminal=false
Categories=Settings;Theme;Colors;Session